1. Field of the Invention
The present invention relates to a variable compression ratio engine wherein one end of a connecting rod is connected to a piston via a piston pin and the other end of the connecting rod is swingably connected to one end of a sub-rod that is in sliding contact with half of the periphery of a crankpin of a crankshaft. A crank cap in sliding contact with the other half of the periphery of the crankpin is secured to the sub-rod, and one end of a control rod is swingably connected to the other end of the sub-rod.
2. Description of the Related Art
Conventionally, such a variable compression ratio engine is already known from, for example, Japanese Patent Application Laid-open No. 2000-73804 in which the position of one end of a control rod connected at the other end to a sub-rod is changed to vary the compression ratio according to the running conditions of the engine.
In this conventional arrangement, the position of the control rod is changed using an electrical or hydraulic device. As a result, the dimensions of the engine increase and the structural arrangement becomes rather complicated. Moreover, in order to operate the electrical or hydraulic device, the engine is required to drive any drive device, which involves a power loss of the engine.
It is an object of the present invention to provide a variable compression ratio engine that allows the position of a control rod to be changed with minimal power loss of the engine while avoiding an increase in the dimensions of the engine and preventing the structural arrangement from becoming complicated.
In accordance with a first aspect of the present invention, there is proposed a variable compression ratio engine wherein one end of a connecting rod is connected to a piston via a piston pin and the other end of the connecting rod is swingably connected to one end of a sub-rod that is in sliding contact with half of the periphery of a crankpin of a crankshaft. A crank cap in sliding contact with the other half of the periphery of the crankpin is secured to the sub-rod, and one end of a control rod is swingably connected to the other end of the sub-rod. The other end of the control rod is swingably connected to a support shaft provided at an eccentric position relative to a rotating shaft that is swingably and axially supported in an engine main body via a one-way clutch. An actuator supported in the engine main body is a diaphragm-type actuator in which the peripheral edge of a diaphragm is sandwiched by a casing. Opposite sides of the diaphragm face a negative pressure chamber that is in communication with an intake passage within a carburetor mounted on the engine main body and an atmospheric pressure chamber that is opened to the atmosphere, respectively. A restricting projection is provided at one location in the circumferential direction on the rotating shaft so as to project outward in the radial direction. A shaft member is provided in the engine main body so that the axis of the shaft member is perpendicular to the rotating shaft. A rocker member mounted on the shaft member is able to rock around the axis of the shaft member and has a pair of engagement portions having phases displaced from each other. The engagement portions can engage the restricting projection and are spring-biased in a direction so that one of the two engagement portions engages the restricting projection. The actuator is connected to the rocker member so as to make the rocker member swing in a direction opposite to the spring-bias direction in response to an increase in the negative pressure of the negative pressure chamber.
In accordance with such an arrangement of the first aspect, a load in a direction in which the control rod is compressed and a load in a direction in which the control rod is pulled alternately act on the support shaft provided on the rotating shaft according to the running cycle of the engine. Therefore, a load to rotate the rotating shaft in one direction and a load to rotate it in the other direction are alternately applied to the rotating shaft. However, the one-way clutch disposed between the rotating shaft and the engine main body only allows the rotating shaft to rotate in one direction. Further, the restricting projection provided on the rotating shaft engages one of the engagement portions provided on the rocker member so that the axis of the shaft member is perpendicular to the rotating shaft. The rocker member is spring-biased in a direction in which one of the engagement portions engages the restricting projection. The rocker member is swung by the actuator in a direction in which the other engagement portion engages the restricting projection. Therefore, the position of the other end of the control rod is changeable between a position corresponding to a high compression ratio and a position corresponding to a low compression ratio. Moreover, since the diaphragm type actuator is operated by the negative pressure of the intake passage within the carburetor, the position of the control rod can be changed with minimal power loss of the engine while avoiding an increase in the dimensions of the engine and preventing the structural arrangement from becoming complicated.
Furthermore, in accordance with a second aspect of the present invention, there is proposed a variable compression ratio engine wherein each engagement portion of the rocker member includes a plurality of steps arranged in the circumferential direction of the rotating shaft so that each of the steps sequentially engages the restricting projection as the rotating shaft rotates. In accordance with such an arrangement, the compression ratio is varied with finer or more accurate differentiation by engaging the restricting projection with the respective steps.
In accordance with a third aspect of the present invention, there is proposed a variable compression ratio engine wherein one end of a connecting rod is connected to a piston via a piston pin and the other end of the connecting rod is swingably connected to one end of a sub-rod that is in sliding contact with half of the periphery of a crankpin of a crankshaft. A crank cap in sliding contact with the remaining half of the periphery of the crankpin is secured to the sub-rod, and one end of a control rod is swingably connected to the other end of the sub-rod. The other end of the control rod is swingably connected to a support shaft provided at an eccentric position relative to a rotating shaft that is swingably and axially supported in an engine main body via a one-way clutch. An actuator supported in the engine main body is a diaphragm-type actuator in which the peripheral edge of a diaphragm is sandwiched by a casing. Opposite sides of the diaphragm face a negative pressure chamber that is in communication with an intake passage within a carburetor mounted on the engine main body and an atmospheric pressure chamber that is opened to the atmosphere, respectively. Engagement portions having phases displaced from each other are provided on the rotating shaft in a plurality of locations in the axial direction. A shaft member is provided in the engine main body so that the axis of the shaft member is perpendicular to the rotating shaft. A restricting member having a restricting projection that selectively engages the plurality of engagement portions is mounted on the shaft member so that the restricting projection is operated within a plane perpendicular to the axis of the shaft member. The actuator is connected to the restricting member to drive the restricting member within the plane that is perpendicular to the axis of the shaft member.
In accordance with such an arrangement of the third aspect, a load in a direction in which the control rod is compressed and a load in a direction in which the control rod is pulled alternately act on the support shaft provided on the rotating shaft according to the running cycle of the engine. Therefore, a load that rotates the rotating shaft in one direction and a load that rotates the rotating shaft in the other direction are alternately applied to the rotating shaft. However, the one-way clutch disposed between the rotating shaft and the engine main body only allows the rotating shaft to rotate in one direction. Further, the engagement portions have phases displaced from each other and are provided on the rotating shaft in a plurality of locations in the axial direction. The engagement portions selectively engage the restricting projection of the restricting member operating within a plane perpendicular to the axis of the shaft member supported on the engine main body so as to have the axis of the shaft member perpendicular to the rotating shaft. The restricting member can be operated by the actuator. Therefore, the position of the other end of the control rod can be changed along a plurality of positions corresponding to a plurality of compression ratios. Moreover, since the diaphragm-type actuator is operated by the negative pressure of the intake passage within the carburetor, the position of the control rod can be changed with minimal power loss of the engine while avoiding an increase in the dimensions of the engine and preventing the structural arrangement from becoming complicated.
Furthermore, in accordance with a fourth aspect of the present invention, there is proposed a variable compression ratio engine wherein the shaft member is supported in the engine main body so as to be able to swing around the axis of the shaft member, and wherein a rack is provided on the restricting member that moves in a direction along the axis of the rotating shaft. The rack meshes with a pinion fixedly provided on the shaft member. In accordance with such an arrangement, the restricting member operates steplessly or continuously in the direction along the axis of the rotating shaft and causes the restricting projection to selectively engage with more engagement portions so as to vary the compression ratio with finer or more accurate differentiation.
The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent from an explanation of preferred embodiments that will be described in detail below by reference to the attached drawings.